The present invention relates to an ion chromatography system comprising a suppressor means which is provided with an exchanging means for exchanging a used ion exchanger with a new ion exchanger every predetermined number of times of measurement, and an ion exchanging means for exchanging automatically a used ion exchanger with a new ion exchanger.
Ion chromatography (hereinbelow, referred to as IC) is a widely used technique to analyze cations or anions in a sample. In IC, an elute is used when such ion species is separated in a separating means such as a separating column. However, when the electric conductivity of the elute is high, a signal of slight amount originated from a desired ion species can not be detected even though an eluted liquid from the separating means is detected by an electric conductivity detector.
Therefore, there has conventionally been proposed such a technique that after a desired ion species has been separated by a separating means; ions in an eluted liquid are substituted by ions of a weak ion type by using means called a suppressor, and then the detection of the desired ion species is conducted.
There have been known suppressors as follows.
(1) A filler bed type suppressor (disclosed in JP-B-56-23100)
(2) A suppressor with an ion exchanging membrane (disclosed in JP-B-62-29024, JP-B-3-68344, JP-B-3-44670 and JP-B-5-48423)
(3) A suppressor for repeating the regeneration of the column (disclosed in JP-B-8-502830 and EP725272B1)
(4) A suppressor for regenerating electrochemically (disclosed in U.S. Pat. No. 5,633,171 and U.S. Pat. No. 5,759,405)
The filler bed type suppressor in (1) is a suppressor comprising a column filled with an ion exchange resin. This suppressor has a problem as follows. A time for analyzing (the number of times of measurements) is restricted inevitably owing to the capacity of the suppressor column since ion exchange groups on the ion exchange resin filled in the suppressor column are substituted by counter-ions in a desired ion species included in a sample or an eluted liquid. When a column having a sufficient capacity is used in order to overcome such disadvantage, there causes a reduction in the resolution ability of the desired ion species. In the determination of nitride, in fact, there has been known that a result of measurement varies remarkably due to the consumption of the suppressor column. In order to conduct the measurement continuously while a reduction in the resolution ability of the ion species is prevented, it is necessary to exchange the suppressor column or regenerate it. However, such exchange or regeneration can not be carried out unless the operation of the liquid transferring means is stopped to release a pressure applied to the flow passage system because the suppressor column is assembled in the flow passage of the chromatography system. Further, there is a problem that the measurement can not be re-opened unless non-abnormality in the flow passage system is confirmed after the exchange of the suppressor column, and unless an inner pressure of the flow passage system being the same as that in the previous measurement is confirmed. The above-mentioned problems are described in Japanese Patent No. 2750002 and JP-A-9-511838.
The membrane type suppressor in (2) is proposed to overcome the problems in the filler bed type suppressor. This suppressor is to obtain a stable suppressing effect even in a case of conducting continuous measurement. Specifically, ions in an eluted liquid are substituted by ions of a weak ion type while the eluted liquid and a regenerating liquid are passed by interposing therebetween an ion exchange membrane, whereby ion exchange groups on the ion exchange membrane, which are substituted by counter-ions of a desired ion species included in a sample or the eluted liquid, are regenerated. Although the membrane type suppressor is capable of conducting continuous measurement for a long time (a large number of times) which is difficult in the filer type suppressor, it is necessary to flow always and stably the regenerating liquid in order to regenerate stably ion exchange groups. Accordingly, a pump or a device of high accuracy is required. Further, there cause problems of environment and cost because a large amount of waste liquid is produced. In addition, since there is a limit in a mechanical strength of the ion exchange membrane, and when a back pressure in the suppressor increases due to any cause, the membrane is broken, whereby the regenerating liquid is mixed with the eluted liquid, with the result that the detection of a desired ion specie becomes impossible. Such problems are described in Japanese Patent No. 2750002 and JP-A-9-511838.
The suppressor for repeating the regeneration of the column in (3) has been proposed to overcome the problem in the filler bed type suppressor in (1). This suppressor has such flow passage system that at least two suppressor columns can selectively be used by using a flow passage switching device so that continuous measuring becomes possible. Specifically, while measurement is conducted by using one of the two suppressor columns, a regenerating liquid is supplied to the other suppressor column, whereby ions in an eluted liquid are substituted by ions of a weak ion type in the former suppressor column, and ion exchange groups on an ion exchange resin are regenerated in the other suppressor column. This suppressor permits continuous measurement for a long time (a large number of times) which was difficult in the filler bed type suppressor in (1), and a reduction in the resolution ability can be suppressed because the capacity per each suppressor column can be reduced. However, since this suppressor has to be operated by switching, in fact, two or three suppressor columns, suppressor requires a pump or a device which passes always the regenerating liquid in a stable manner, to regenerate the suppressor columns in a short time. Further, there cause problems of environment and cost because a large amount of waste liquid is produced. In addition, there is a problem that the ion exchange resin filled in the suppressor columns is stained by a certain kind of heavy metal or organic material during a repetitive use for a long term, whereby a regenerating liquid used usually (e.g., 20 mmol/l of H2SO4 and NaOH) can not provide a sufficient regeneration, and a suppressing performance is reduced.
The suppressor for regenerating electrochemically in (4) is such that an eluted liquid from one suppressor column is introduced into the other suppressor column, and then, the eluted liquid from the later is regenerated by electrolysis. In this suppressor, however, there is a problem that due to a limitation by the relation between the area of electrodes and an applied voltage, an inner shape of the suppressor causes a reduction in the resolution ability of to a desired ion species.
It is an object of the present invention to provide an ion chromatography system capable of conducting continuously a large number of times of measurement to measure with a high sensitivity a slight amount of ion species in a sample without the necessity of passing continuously the regenerating liquid, hence, minimizing the discharge of waste liquid, and without causing a reduction in the suppressing effect or a reduction in the resolution ability of a desired ion species.
It is an object of the present invention to provide an ion exchanging means for exchanging automatically a used ion exchanger with a new ion exchanger.
In accordance with an aspect of the present invention, there is provided an ion chromatography system wherein a desired ion species in a sample is separated by a separating means; an eluted liquid from the separating means is introduced into a suppressor means, in which an ion exchanger is held, to reduce the electric conductivity of the eluted liquid, and the eluted liquid from the suppressor is introduced into a detector to detect desired ions, the ion chromatography system being characterized in that the suppressor means is provided with a main body for accommodating an ion exchanger ready for measuring; a chamber for accommodating a virgin ion exchanger, and an automatic exchanging means which discharges a used ion exchanger from the main body after an optional number of times of measurements and supplies the ion exchanger accommodated in the chamber to the main body.
According to the present invention, there is provided the ion chromatography system according to the first aspect wherein the suppressor means comprises a 6-way switching rotary valve having 3 rotary grooves a, b and c, a chamber for accommodating a virgin ion exchanger in a slurry state, a liquid transferring tank which accommodates a transferring liquid for introducing the ion exchanger in a slurry state in the chamber into the rotary valve, and a liquid transferring means for supplying the transferring liquid; a flow passage from the separating means is connected to a flow passage to the detector by means of the rotary groove a; a flow passage from the liquid transferring means to the chamber is connected to a flow passage to a third rotary groove by means of the rotary groove b; a flow passage from the rotary groove b is connected to a flow passage to the outside of the main body by means of the rotary groove c, and each filter which prevents the ion exchanger from passing through is provided at a side of the separating means with respect to the rotary groove a, at a side of the detecting means with respect to the rotary groove a and at a side of the rotary groove c with respect to the rotary groove b.
According to the present invention, there is provided the ion chromatograph system according to the first aspect wherein the suppressor means comprises a tube having both ends which are tightly closed with sealing materials capable of passing only a string-like ion exchanger; a chamber for accommodating a virgin string-like ion exchanger, and a supply means which introduces the string-like ion exchanger in the chamber into the tube from its one end and discharges it from the other end of the tube; a portion in the vicinity of one end of the tube is connected to a flow passage from the separating means, and a portion in the vicinity of the other end of the tube is connected to the detecting means.
According to the present invention, there is provided the ion chromatography system according to the first aspect wherein the exchanging means is to replace the used ion exchanger by a new ion exchanger every predetermined number of times of measurement.
According to the present invention, there is provided the ion chromatography system according to the first aspect wherein the ion exchanger is an ion exchange resin or ion exchange fibers.
In accordance with a second aspect of the present invention, there is provided an ion exchanging means for holding an ion exchanger which comprises a holding section for accommodating an ion exchanger ready for measuring, a chamber for accommodating a virgin ion exchanger, and an automatic exchanging means which discharges a used ion exchanger from the main body after an optional number of times of measurements and supplies the ion exchanger accommodated in the chamber to the main body.
According to the present invention, there is provided the ion exchanging means according to the second aspect, wherein the ion exchanging means comprises a 6-way switching rotary valve having 3 rotary grooves a, b and c, a chamber for accommodating a virgin ion exchanger in a slurry state, a liquid transferring tank which accommodates a transferring liquid for introducing the ion exchanger in a slurry state in the chamber into the rotary valve, and a liquid transferring means for supplying the transferring liquid.
According to the present invention, there is provided the ion exchanging means according to the second aspect, wherein the ion exchanging means comprises a tube having both ends which are tightly closed with sealing materials capable of passing only a string-like ion exchanger; a chamber for accommodating a virgin string-like ion exchanger, and a supply means which introduces the string-like ion exchanger in the chamber into the tube from its one end and discharges it from the other end of the tube.
According to the present invention, there is provided the ion exchanging means according to the second aspect, wherein the exchanging means is to replace the used ion exchanger by a new ion exchanger every predetermined number of times of measurement.
According to the present invention, there is provided the ion exchanging means according to the second aspect, wherein the ion exchanger is an ion exchange resin or ion exchange fibers.